Contribution of Organic Anion Transporter 3 in Delayed Elimination of Methotrexate by Concomitant Administration of Febuxostat.

Methotrexate is an antifolate agent used for the treatment of various malignancies and is mainly secreted via human organic anion transporter 3 (hOAT3) in the proximal tubular cells. Coadministration of the xanthine oxidase inhibitor, febuxostat, in patients receiving methotrexate has been reported to be associated with an elevated risk of hematological toxicity and increased plasma methotrexate levels. Because febuxostat has an inhibitory effect against hOAT3, it may inhibit renal elimination of methotrexate via hOAT3. However, the drug interaction between methotrexate and febuxostat via hOAT3 remains to be clarified. In the present study, we investigated the effect of febuxostat on pharmacokinetics of methotrexate in rats and drug interaction between methotrexate and febuxostat using hOAT3-expressing cultured cells. In the pharmacokinetics study using rats, concomitant administration of febuxostat significantly increased plasma concentration of methotrexate and prolonged its half-life. In vitro studies showed that febuxostat inhibited hOAT3-mediated transport of methotrexate in a concentration-dependent manner. Dixon plot indicated that inhibitory constant value of febuxostat against methotrexate transport via hOAT3 was 0.63 ± 0.01 μM. Moreover, the inhibitory effect of febuxostat was of noncompetitive type. Taken together, these results suggest that concomitant administration of febuxostat delayed elimination of methotrexate, at least in part, by noncompetitive inhibition of hOAT3-mediated methotrexate transport at clinical concentrations. The findings of this study provide novel information on drug interactions associated with febuxostat.